/Engine/Source/Runtime/CoreOnline/Public/Online/CoreOnline.h
A handle to an id which uniquely identifies a persistent or transient online resource, i.e. account/session/party etc, within a given Online Services provider. At most one id, and therefore one handle, exists for any given resource. The id and handle persist until the OnlineServices module is unloaded. Passed to and returned from OnlineServices APIs.
template<typename IdType> class TOnlineId